CSVHandler

Golang built-in encoding/csv package can be tedious to use as it handles records as low level types []string, forcing users to access field using indexes.
This package aims to ease this use by allowing direct access with the column name, with an API close to encoding/csv.

For a usage closer to encoding/json with marshal/unmarshal functions to/from a struct, consider using other package such as github.com/jszwec/csvutil or github.com/gocarina/gocsv.

Installation

go get github.com/jcuvillier/csvhandler

Reader

csvInput := bytes.NewBuffer([]byte(`
first_name,last_name,age
Holly,Franklin,27
Giacobo,Tolumello,18`,
))

reader, _ := csvhandler.NewReader(csv.NewReader(csvInput))
record, _ := reader.Read()
record.Get("first_name") // returns Holly
record.GetInt("age")     // return 27

Writer

// Create a writer to stdout with header "first_name,last_name,age"
writer, _ := csvhandler.NewWriter( csv.NewWriter(os.Stdout), "first_name", "last_name","age")

// Write header line
writer.WriteHeader() // Writes first_name,last_name,age

// Create a record to be written
record := NewRecord()
record.Set("first_name", "Holly")
record.Set("last_name", "Franklin")
record.Set("age", 27)
writer.Write(record) // Writes Holly,Franklin,27

Empty and default values

If a field is not specified, Writer.EmptyValue is used. A default value can also be provided with Writer.SetDefault function.

writer, _ := csvhandler.NewWriter( csv.NewWriter(os.Stdout), "first_name", "last_name","age")
writer.SetDefault("age", 18)

record := NewRecord()
record.Set("first_name", "Holly")
writer.Write(record) // Writes Holly,,18

Formatter

Formatters can be defined and used when writting records.

// Formatter is the function that returns a string formatted version of the given value or an error.
type Formatter func(interface{}) (string, error)

Built-in formatters

This library provides built-in formatters:

• StringFormatter

// StringFormatter returns a new formatter that uses the given format.
// Format is applied using `fmt.Sprintf`
func StringFormatter(format string) Formatter

• TimeFormatter

// TimeFormatter returns a new formatter that uses the given layout to format a time.
// Only time.Time and *time.Time are allowed as value for the returned formatter.
func TimeFormatter(layout string) Formatter

How to specify formatter ?

Formatters can be specified when setting a value to a record

record.Set("first_name", "Holly", StringFormatter("My name is %v")) // My name is Holy

or when setting a default value

writer.SetDefault("age", 18, StringFormatter("%v (default)")) // 18 (default)

If no formatter is specified, the following defaultFormatter is applied:

// defaultFormatter is the formatter used when no formatter are specified by caller.
// It printfs the value with a basic `fmt.Sprintf("%v")`
func defaultFormatter(value interface{}) (string, error) {
	return fmt.Sprintf("%v", value), nil
}

It is also possible to specify a formatter to be applied for a given column, this formatter is chained with any formatter previously specified.

writer.SetFormatter("last_update", TimeFormatter(time.UnixDate)) // Tue Jan 26 10:20:08 CET 2021

Chained formatter

Formatters are passed using a variadic to make it optionnal. Therefore it is possible to specify multiple formatter, in such case, they are chained.

record.Set("time", time.Now(), TimeFormatter("Monday 02 Jan 2006"), StringFormatter("Today is %v")) // Today is Tuesday 26 Jan 2021

Record

Get fields

Record holds the fields for a given entry.
It offers utility functions to Get field based on the column name to a given type, for instance:

GetInt(key string) (int, error)

Supported types are string, bool, int, int64, float64, time.Time and timne.Duration.

Print fields

You can also print as key/value pairs a record by giving the column name.

r.Println("first_name", "last_name") // prints to stdout "first_name='Holly' last_name='Franklin'"